The invention relates to an adsorbent for selectively removing nitrites from a hydrocarbon feedstock, to a method for making the adsorbent, and to a process for removing nitrile from a hydrocarbon feedstock using the adsorbent.
Nitrile compounds are frequently undesirable contaminants in feedstocks which otherwise contain valuable fractions. Particularly, C4 and C5 cuts from FCC units can be useful in the preparation of oxygenates such as MTBE, ETBE, TAME and the like. However, these feedstocks typically contain nitriles and diolefins. The diolefins may typically be hydrogenated before and/or at the etherification reactor. Nitriles, however, must be removed upstream of the reactor and therefore must be removed in the presence of dienes which make the feedstock highly reactive.
Upstream nitrile removal techniques include washing, but propionitrile cannot be removed through washing. In the presence of hydrogenation catalysts, however, propionitrile is believed to undergo conversion to totally or partially hydrogenated products, which behave as basic nitrogen and rapidly poison the acid sites of the etherification catalyst. It is apparent that the need remains for a treatment for removal of nitrile compounds, especially propionitrile, wherein the agent used for removal is selective to nitrile and has longevity toward the selective removal of nitrile especially in the presence of relatively large amounts of dienes.
In addition, under adsorption conditions for treating such reactive feedstock, the adsorbent used retains the removed nitriles and other contaminants. It is desirable to provide a desorption process, which process removes the contaminants without damaging the adsorbent so that it can be returned to adsorption conditions for extended periods of time.
It is therefore the primary object of the present invention to provide a nitrile selective adsorbent which is not rapidly deactivated during use, even in the presence of dienes.
It is a further object of the present invention to provide a desorption method for removing retained contaminants from the adsorbent.
It is a still further object of the present invention to provide a suitable desorbent for removing retained contaminants from the adsorbent.
It is another object of the present invention to provide a process for treating a feedstock such as an FCC C4-C7 feedstock with a nitrile selective adsorbent according to the invention so as to effectively and selectively remove nitrile compounds wherein the adsorbent can be restored using a selective desorbent.
It is still another object of the present invention to provide a desorption process for restoring such an adsorbent to adsorption condition for extended periods of time.
Other objects and advantages will appear herein below.